Purity and blue lateral assembly for delta beam type cathode ray tube

ABSTRACT

A static magnetic assembly for delta beam type cathode ray tubes for providing proper convergence adjustment of the electron beams.

United States Patent [191 Poel 1 Dec. 25, 1973 PURITY AND BLUE LATERALASSEMBLY FOR DELTA BEAM TYPE CATHODE RAY TUBE [76] Inventor: Lawrence R.Fuel, 6620 Mesa Grande, El Paso, Tex.

22 Filed: Mar. 23, 1973 21 App1.No.:344,222

[52] US. Cl. 335/212, 313/77. [51] Int. Cl H01f [58] Field of Search335/210, 212;

Primary ExaminerGeorge Harris Att0mey-Le0 J. Aubel [5 7] ABSTRACT Astatic magnetic assembly for delta beam type cathode ray tubes forproviding proper convergence adjustment of the electron beams.

10 Claims, 7 Drawing Figures PURITY AND BLUE LATERAL ASSEMBLY FOR DELTABEAM TYPE CATHODE RAY TUBE BACKGROUND OF THE INVENTION As is known,delta gun, tri-color kinescopes or cathode ray tubes (CRT) used forcolor television receives include an electron gun assembly having threeseparate electron guns positioned in a triangular configuration toprovide three distinct relatively triangularly disposed beams whichimpinge on the viewing screen of the CRT or picture tube. The CRTcomprises a screen made up of three different color phosphor dots,arranged in the form of triads, each consisting of a blue phosphor dot,a red phosphor dot and a green phosphor dot. The dots are positionedrelatively close together, without overlapping or touching each other,and each of the three beams is arranged to respectively strike onlythose phosphor dots of a particular color.

Again, as is known, when a beam strikes a phosphor dot, that dot willemit light with its respective color; that is, the blue phosphor dotwill emit light with a blue color, etc. The characteristics of the humaneye are such that the individual light emissions from the three phosphordots are normally not distinguishable; and, the eye will blend theindividual light output of the phosphor dots into a single output. Bycontrolling the light output of the respective phosphor dots, a varietyof colors which corresponds to the colors in the visible light spectrumare produced.

The delta gun tri-color tube further includes an aperture or shadowmask, which consists of a thin sheet with a series of small holes.'Theshadow mask covers the entire viewing screen and includes as many holesas there are phosphor triads on the screen; that is, each hole on theshadow mask corresponds to a dot triad on the viewing screen. Asmentioned above, the electron beams from the three guns are arrangedtobe directed at an angle through each hole such that each beam willenergize the same colored dot in each triad throughout theviewingscreen. The three electron beams are therefore controlled toconverge at the holes of the aperture mask and diverge at the properangle to impinge upon its respective dot, such that as mentioned, theblue beam impinges only upon a blue phosphor dot, etc.

Since each beam must impinge upon its respective phosphor dot, the beamsmust be individually controlled to provide a desired color output. Thethree beams provided by the electron gun assembly are in as closealignment as the state of the art will allow with each other and withthe central axis of the tube before they pass through the convergencefield. However, because of production tolerances, variations in the gunstructure, and differences in the voltage applied thereto, the electronbeams may not be in perfect alignment with each other. A common exampleis that the gun assembly may be rotated slightly relative to the axis ofthe neck of the tube and hence, will be skewed relative to the viewingscreen and, hence, the beams will not impinge at the proper point on theviewing screen. Also, as another example, the three beams may not beproperly aligned with respect to the central axis of the tube.Accordingly, should the beams enter the area of deflection at animproper point the blue beam may for instance, tend to impinge, in part,on the red or green color phosphors and the purity of the colorswill beimpaired. i I

Thus, it will be appreciated that both static convergence devices anddynamic control devices must be provided to the beams to properlydirect, position and deflect the beams vertically and horizontally tocover the entire viewing screen.

The present invention is particularly directed to a purity and bluelateral control static magnetic convergence assembly. More specifically,in the type of CRT mentioned, it is necessary to adjust the position ofthe beam with respect to the aperture mask in the viewing screen byusing auxiliary components such as blue lateral correction assembliesand purity magnets. While the prior art discloses various types of bluelateral connection assemblies and purity magnets, such prior art deviceshave for one reason or another, not been entirely satisfactory.

Accordingly, it is a principal object of the present invention toprovide an improved purity and blue lateral assembly for delta beamcathode ray tubes.

It is another object of the present invention to provide a staticmagnetic assembly which provides a more precise and accurate adjustmentand control of the three beams of a delta gun cathode ray tube.

It is known in the art, and can be verified geometrically, that any twoof the three beams, say the red and green beams can be converged in astraight line directly toward the center axis of the neck of the tube;and, the beams cannot all be directly converged. Therefore, a specificmagnetic field is provided by the so-called blue lateral correctionmagnet, to move the blue beam in a horizontal direction to converge theblue beam with respect to the red and green beams.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of embodiments of the invention, as illustrated in theaccompanying drawings wherein:

DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view showing theinventive purity and blue lateral assembly in accordance with theinvention;

FIG. 2 is a side view of the inventive assembly shown mounted on theneck of an associated cathode ray tube;

FIG. 3 is a front view of the inventive assembly shown mounted on theneck of the associated cathode ray tube; and, FIG. 3 includes a showingof the lines of force of the magnetic fields developed by the inventiveassembly;

FIG. 4 is an exploded view showing some of the pole pieces'or pole pieceextenders utilized in the present invention;

FIG. 5 shows the ferrite rod used in the present invention; and showsthree permanent magnets formed thereon;

FIG. 6 is a side view showing mounting means for the rod; and,

FIG. 7 is a view partly in section showing a mounting of the pole pieceextenders on an associated stud.

DESCRIPTION OF THE INVENTION Refer now to the'Figures. The overallphysical construction of the inventive purity and blue lateral assembly11 is clearly shown in FIGS. l-3.

Before describing the structure of FIGS. 1-3, note that the inventivepurity and blue lateral assembly functions to adjustably cause theposition of the 'blue beam to cause the red and green beams toadjustably and correspondingly move in an equal and opposite directionrelative to the blue beam.

The purity and blue lateral assembly 11 of the invention comprises aplastic or nonmagnetic carrier or base 12 formed in a planar surfacewhich includes a central clamping flange 15A and a central aperture 15to permit the mounting of the blue lateral assembly 11 on the neck 13 ofthe associated CRT as by a suitable clamp 42. In the FIG., the blue andgreen beams are shown in their approximate operating position.

Blue lateral assembly 11 includes ferrite rod 19 mounted in a horizontalorientation on base 12, see also FIGS. and 6. The ferrite rod 19includes a first or central magnet portion 22 polarized across adiameter of the rod in a first orientation relative to the principalaxis of the tube to provide a magnetic field component transverse to thepath of the blue beam, as will be explained. Rod 19 further includes apair of additional magnet portions 21 and 23 which are disposed adjacentto, but on opposite sides of magnet portion 22. Magnets 21 and 23 arealso polarized across a diameter of the rod but at a 180 angle relativeto the orientation to magnet 22. Magnets 21 and 23 provide magneticfield components transverse to the paths of the red and green beams aswill also be explained.

In, one embodiment, magnets 21 and 23 have substantially equal fieldstrengths and magnet 22 has a field strength less than magnets 21 and23. Magnets 21, 22 and 23 may be formed by selectively magnetizing asingle ferrite rod or may be formed individually and in tergrated into asingle cylindrical structure. The strengths of the three beams may beselected and adjusted to develop a resultant magnetic field of desiredconfiguration and strength.

The ferrite rod ismounted on the base 12 such as by two spacedupstanding flanges 24 having semi-circular shaped recesses 26, andhaving slightly yieldable end portions. Rod 19 forcefully pushed intorecess 26 is retained therein.

A circular thumbwheel 28 element of nonmagnetic material, having acentral hole 32 is mounted on ferrite rod 19. Rod 19 fits tightly in"hole 32 and rotation of thumbwheel 28 permits rotatable movement of rod19. Base 12 includes a hole which receives and permits free rotation ofthumbwheel 28. As will be obvious, thumbwheel 28 can be manuallyadjusted to obtain the desired fine positioning of the north and southmagnets-of rod 19, for purposes to be explained.

The purity magnets control the beams such that each beam strikes onlyits respective set of phosphor dots to cause individual registry of therasters. The purity magnets comprise two rings 44 and 46 composed ofmag-- I netic material and arranged for mounting around the neck 13 ofthe CRT. The individual rings are polarized such that one-half of eachring is of a positive or north polarity and the opposite one-half of thering is of a negative or south polarity; and, each of the rings isarranged to be rotated about the central axis of the tube. The rings areplaced adjacent to each other such that the field developed by one ringcan either augment or substract from the field developed by the otherring. Thus, the strength of the field existing in the space at thecenter of the rings, and hence, in the center of the tube in the spaceof aperture which the electron beams traverse, may. be varied. Forexample, the field in the center of the ring may have maximum strengthwhen the ring portions of like polarities of the two rings 44 and 46 areadjacent to each other. And, as one magnet is rotated relative to theother, the magnetic field is decreased, in strength. The field producedby the two rings is essentially uniform and exerts an approximatelyequal force on all three beams with the force being at right angles tothe direction of the magnetic field. With proper rotatable adjustment ofone or both purity magnets, such as by manually moving tabs 48 and 49formed on rings 44 and 46 respectively, the grouped electron beams canbe caused to enter the static deflection fields at the proper point suchas to pass-through the shadow mask at the proper angles to produce apure color.

The configuration of the pole piecesub-assembly is an important aspectof the invention and will now be described.

The pole piece sub-assembly, generally labeled 30, comprises pole piecemembersor extenders 31, 32, 33, 34, 35, 36, 37 and 38, each formed of alow cocrcivity metal ribbon, see FIG. 3 and FIG. 4. The pole pieces31-38 are mounted in suitably positioned, vertically split stud members18 formed on base 12, see FIGS. 3 and 7. The narrow width of sections ofthe ribboned pole pieces are wedged into the split 20 of the studmembers 18.

For purposes of this explanation, the inventive assembly 11 may beconsidered to have a vertical axis 40 as indicated in FIG. 3, and thepole piece sub-assembly 30 is symmetrical about axis 40 as will becomeclear. For purposes of this description, the top of the aperture 15through which axis 40 passes will be considered as zero degrees (0) ofthe circle formed by aperture 15.

Pole piece or pole piece extenders 31 and 38 are the larger of the polepieces and are positioned farthest from aperture 15. Pole pieces 31 and38 are mirror images one of the other; and, hence a description of polepiece 31 is necessary only. Pole piece 31 is essentially of a modifiedC-shape with the upper part of the C- shape forming a horizontalsection, and having a vertical depending free end portion. The tip ofthe free end portion is positioned adjacent the north magnetic pole ofthe center magnet 22. The bight portion of pole piece 31 extendsdownwardly at an angle of about 17l.5 with the vertical axis 40. Thelower part of the C-shape pole piece 31 is a section which extends at anangle of about 106.5 with respect to the vertical axis 40; and, the freeend thereof is mounted to be tangential to the aperture 15. The lowertip of pole piece 31 terminates at about 185 on the periphery of thecircle of aperture 15.

As noted above, the pole piece 38 is mounted on the other side of theaxis 40 in mirror image position relative to pole piece 31 and aperture15. The lower tip of pole piece 38 terminates at about on the periphery.of the circle of aperture 15. The tips of upper ends of i the northpole of magnet 22. The bight portion of pole piece 32 extends downwardlyat an angle of about 17 1 .5 with respect to the 0 axis 40. The lowerpart of pole piece 32 extends at an angle of about I l4.5 with respectto the axis 40 and the lower tip of pole piece 32 terminates at theperiphery of aperture at approximately 225 relative to the circle ofaperture 15.

Pole pieces 33 and 36, which are mirror images one of the other,comprise essentially an inverted L-shape. Again, since pole pieces 33and 36 are essentially identical a description of pole piece 33 only isnecessary. The horizontal portion of the pole piece 33 is in contactwith the south pole of magnet 22. The vertical portion of the L-shapeextends downwardly at an angle of approximately 83 with axis 40 and thelower tip of pole piece 33 terminates at the periphery of the circle ofaperture 15 at approximately 292.5.

The center pole pieces 34 and 35 are the smallest of the pole pieces 30and comprise an inverted L-shape configuration. Again, pole pieces 34and 35 are essentially identical and are positioned to form mirrorimages, one of the other. The horizontal portion of pole piece 32 abutsand its vertical leg extends downwardly at an angle of l64.5 withrespect to the axis 40 and terminates at about 350 on the periphery ofthe circle of aperture 15.

The magnets 21, 22 and 23 and the pole piece 30 form in the spaceencompassed by aperture 15, a composite magnetic field marked generallyby the Greek letter theta (0). The magnetic lines of force of a firstsubfield Ol-L may be traced from the north pole of the magnet 22 downpole piece 34 extending through the space traversed by the blue beam Bdown to the lower tip of pole piece 31 and the south pole of magnet 22.

A similar and symmetrical subfield 01-R may be traced from the northpole of magnet 24 down pole piece 34 to the lower tip of pole piece 38,then upwardly through pole piece 38 to the south pole of magnet 22.

The fields 01-L and 0l-R effectively combine their magnetic force toprimarily affect the blue beam as will be explained.

Another subfield 02-L may be traced from the northpole of magnet 22through pole piece 34, and from the tip of pole piece 34 across aperture15 to the lower tip of pole piece 33 up through the pole piece 33 to thesouth pole of magnet 22, and thence, to the north pole of magnet 22. Asimilar subfield 02-R which is symmetrically with respect to field 02-1.extends across aperture 15 from pole piece 35 .to pole piece 36.

. Another subfield 03-L'may be traced from the north pole of magnet 21through pole piece 32 to the lower tip thereof, across aperture 15 tothe lower tip of pole piece 33, and upwardly through pole piece 33 tothe south pole of magnet 21. Field 03-L primarily affects the red beam.A similar field 03-R which is symmetrically with respect to field 63-Lmay be traced from the lower tip of pole piece 37 across aperture 15 tothe tip of pole piece 36. Field 03-R primarily affects the green beam.

A fourth subfield 04-L extends across aperture 15 from the lower tipofpole piece 32 to the lower tip of pole piece 31. A similar andsymmetrical subfield 04-R extends from the tip of pole piece 37 to thelower tip of pole piece 38.

In the space which the blue beam traverses, the lines of force of fieldsOl-L and 0I-R, which primarily affect the blue beam, extend essentiallyparallel to the vertical axis 40. The field 03-L primarily affects thered beam and has a principle component in a vertical direction in thatspace which the red beam normally traverses. Likewise, field 03-R has aprinciple component in a vertical direction in that space which thegreen beam normally traverses.

The orientation of the lines of force or flux polarity of the fieldsOl-L and Ol-R in the space of aperture 15 is from a north to southdownward direction as shown in FIG. 3, and the direction of the fields63-1.. and 03-R which affect the red and green beam is in a relativereversed direction, that is, in a north to south upward direction. Thefields 02-L and 6 2-R are essentially fringe fields and have minoreffect on the control of the three electron beams.

The operation of the inventive assembly 11 can now be considered. Assumethe electron beam current flows through the neck 13 of the CRT in adirection outwardly of the paper. In accordance with the well knownright hand motor rule for electrical flow, the field 01-R and OI-Lprovided by assembly 11 jointly develop a motion vector labeled M forthe blue beam which is directed toward the left as indicated in theFigure. Conversly, since the polarity of fields 03 are in an upwarddirection, a motion vector M for the red and green beams will bedeveloped directed toward the right as indicated in the Figure.

The relative field strengths are adjusted such that the blue beam willmove equally and oppositely to the red and green beams. As mentionedabove, in one embodiment, magnets 21 and 23 are arranged to havesubstantially equal field strengths and magnet 22 has a field strengthless than magnets 21 and 23.

Relative left and right motion of the blue beam is achieved by rotationof the magnet rod 19 such as by moving thumbwheel 28 to vary thestrength of the magnetic fields 0 developed in aperture 18. Note that lrotation of rod 19 provides a reversal of relative direction of themagnetic flux coupled to the pole piece subassembly. Thus, by rotationof the rod, l80 relative to the position shown in FIG. 3, the blue beamis movable in a relatively opposite direction or toward the right asindicated in FIG. 3. Likewise, the red and green beams would then bemoveable in an opposite direction or toward the left as orientated inthe Figure.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention. For example, known different adjustment means, for ferriterod in lieu of thumbwheel 28 could be utilized; also, the lower ends ofpole piece extenders 31, 32, 33, 34, 35, 36, 37 and 38 located aroundthe neck of the CRT may be positioned at different locations while therelative strength between the magnets 21, 22 and 23 may be varied tocause essentially the same motion as herein previously described. Also,while the ends of the pole piece members terminate along the peripheryof the tube neck at approximately 10, 65, 225, 295, and 350; the exactpositioning thereof may be varied within empirical tolerances withoutadversely affecting the operation of the apparatus.

What is claimed is:

1. Convergence apparatus for mounting on the neck of a cathode ray tubehaving a triangular arrangement of three electron beams passing throughthe neck of the tube, said apparatus comprising an array of at leastthree magnets, pole piece assemblies selectively coupling magneticallyto said magnets, said pole piece assemblies each comprising elongatedlow coercivity members, said members having one end positioned-adjacenta respective magnet, and in operating condition, the other end of saidmembers positioned in spaced pe ripheral relation one to the other,adjacent the neck of the cathode ray tube to develop a first magneticfield having principle components traversing the path of the first beam,a second magnetic field having principle components traversing the pathof the second beam, and a third magnetic field having principlecomponents traversing the path of the third beam.

2. Convergence apparatus as in claim 1 wherein a first field has linesof force extending downwardly in a north to south polarity in the pathwhich said first beam traverses and said second and third field lines offorce extending upwardly in a north to south polarity in the path whichsaid second and third beams traverse.

3. Convergence apparatus as in claim 1 wherein said magnets comprise arod positioned substantially along a horizontal axis and wherein saidmagnets have a polarity orientation in substantially a vertical axis.

4. Convergence apparatus as in claim 1 for controlling and varying theposition of said three beams wherein the magnet affecting the first beamis of less strength than the magnets affecting the two other beams.

5. Convergence apparatus as in claim 1 wherein there are a total ofeight pole piece members, said pole piece members positioned in spacedrelation around the periphery of said neck, and wherein four of saidpole piece members provide a path for magnetic fields for affecting theposition of the first beam, two of said pole piece members develop afield for affecting a second one of the beams and two pole membersdevelop a field for affecting the third beam.

6. Convergence apparatus as in claim 1 wherein said pole piece memberscomprise ribbon-like, low coercivity metal.

7. Convergence apparatus as in claim 1 wherein said magnets are formedas a rod, means for rotating said rod to control the lines of forcedeveloped in the pole piece members.

8. A convergence apparatus as in claim 1 wherein the end of said polepiece members are positioned around the periphery of said neck atapproximately 10, 65, 225, 295, and 350.

9. Convergence apparatus as in claim 1 wherein said magnets and saidpole piece members are mounted on a substrate having an aperture thereinfor mounting on the neck of a cathode ray tube.

10. Convergence apparatus as in claim 1 wherein said pole piece membersare in mechanical contact with said rods and are positioned in spacedrelation one to the other.

1. Convergence apparatus for mounting on the neck of a cathode ray tubehaving a triangular arrangement of three electron beams passing throughthe neck of the tube, said apparatus comprising an array of at leastthree magnets, pole piece assemblies selectively coupling magneticallyto said magnets, said pole piece assemblies each comprising elongatedlow coercivity members, said members having one end positioned adjacenta respective magnet, and in operating condition, the other end of saidmembers positioned in spaced peripheral relation one to the other,adjacent the neck of the cathode ray tube to develop a first magneticfield having principle components traversing the path of the first beam,a second magnetic field having principle components traversing the pathof the second beam, and a third magnetic field having principlecomponents traversing the path of the third beam.
 2. Convergenceapparatus as in claim 1 wherein a first field has lines of forceextending downwardly in a north to south polarity in the path which saidfirst beam traverses and said second and third field lines of forceextending upwardly in a north to south polarity in the path which saidsecond and third beams traverse.
 3. Convergence apparatus as in claim 1wherein said magnets comprise a rod positioned substantially along ahorizontal axis and wherein said magnets have a polarity orientation insubstantially a vertical axis.
 4. Convergence apparatus as in claim 1for controlling and varying the position of said three beams wherein themagnet affecting the first beam is of less strength than the magnetsaffecting the two other beams.
 5. Convergence apparatus as in claim 1wherein there are a total of eight pole piece members, said pole piecemembers positioned in spaced relation around the periphery of said neck,and wherein four of said pole piece members provide a path for magneticfields for affecting the position of the first beam, two of said polepiece members develop a field for affecting a second one of the beamsand two pole members develop a field for affecting the third beam. 6.Convergence apparatus as in claim 1 wherein said pole piece memberscomprise ribbon-like, low coercivity metal.
 7. Convergence apparatus asin claim 1 wherein said magnets are formed as a rod, means for rotatingsaid rod to control the lines of force developed in the pole piecemembers.
 8. A convergence apparatus as in claim 1 wherein the end ofsaid pole piece members are positioned around the periphery of said neckat approximately 10*, 65*, 135*, 175*, 185*, 225*, 295*, and 350*. 9.Convergence apparatus as in claim 1 wherein said magnets and said polepiece members are mounted on a substrate having an aperture therein formounting on the necK of a cathode ray tube.
 10. Convergence apparatus asin claim 1 wherein said pole piece members are in mechanical contactwith said rods and are positioned in spaced relation one to the other.